Earlier quoted context omitted.
Turbolinks can create problems even to those who don't use them explicitly, but Coffeescript can't: if you don't like it, just don't use it, and it's as if it wasn't there. How would removing it from the asset compiler help you in any way?
There's a cultural impact - it's hard to look at Rails without being pushed in that direction. Does it directly impact me now that I choose to ignore it? No. Does it impact a newcomer, particularly one that's into JS? Yes.
It's not perfect but it's how I learned coffeescript.
Other than that, I don't think Rails necessarily pushes either for/against coffeescript. You can either use it or not. Plenty of rails apps have been written in plain 'ol js.